As to fuel cell separators, two major groups, i.e. metallic separators and carbon separators, are now under study.
Noble metals such as gold, etc. are desirable for the metallic separators from the viewpoint of electrochemical stability, but are very expensive and thus are not yet practicable. Other metals, such as iron, etc. have a problem of electrochemical corrosion, requiring surface coating with a noble metal, and thus still have such a disadvantage as processwise high cost.
Carbon separators, on the other hand, are electrochemically stable. Graphite substrates are prepared by a process of impregnating a thermosetting resin such as phenol resin, furan resin, etc. followed by calcining or by a process of kneading graphite powder with a thermosetting resin, followed by molding into a plate form and successive calcining. The graphite substrates are not only expensive because these processes require a calcining step for carbonization or graphitization to obtain a high electroconductivity, but also post-processing is indispensable for formation of cooling water passages, etc.